The subject matter disclosed herein relates to heating systems. More specifically, the subject disclosure relates to burners for residential and commercial heating systems.
Heating systems, in particular furnaces, include one or more burners for combusting a fuel such as natural gas. Hot flue gas from the combustion of the fuel proceeds from the burner and through a heat exchanger. The hot flue gas transfers thermal energy to the heat exchanger, from which the thermal energy is then dissipated by a flow of air driven across the heat exchanger by, for example, a blower.
A typical construction is shown in FIG. 1. A burner 100 is located external to a heat exchanger 102. The burner 100, referred to as an inshot burner 100, receives a flow of fuel from a fuel source 104. An ignition source 106 combusts the flow of fuel. Even though the inshot burner 100 is in close proximity to heat exchanger 102, surfaces of the heat exchanger 102 adjacent to the combustion flame 110 are kept relatively cool by a flow of secondary air 108 to prevent damage to the surfaces of the heat exchanger 102 via the combustion flame 110.
Another type of burner is a premix burner in which fuel and air are mixed in the burner nozzle prior to injection into a combustion zone 112 where the ignition source 106 ignites the mixture. Premix burners, compared to inshot burners, typically emit much lower levels of NOx, the emissions of which are tightly regulated and restricted in many jurisdictions. Because of this typical advantage of premix burners, it is often appealing to introduce premix burners into furnaces. However, a premix burner having physical and operating characteristics similar to the burner 100 may not be suitable for use with heat exchanger 102. The heat exchanger walls and cell panel 103 would necessarily be in close proximity to the burner and thus the concentration of heat produced in the immediate vicinity of the burner would typically result in excessively high temperatures in the wall of the heat exchanger 102 and cell panel 103. Such high temperatures would typically increase the surface temperatures of the surrounding heat exchanger 102 and cell panel 103 and, thereby, may shorten the life of the heat exchanger 102 and cell panel 103. Further, premix burners typically have a much quicker heat release than inshot burners and generally do not have the benefit of secondary airflow to cool the heat exchanger surfaces and, thereby, protect them from damage. Thus, simply replacing inshot burners with premix burners in an existing furnace construction would typically result in excessively high temperatures at adjacent heat exchanger surfaces.